An example of a solid electrolytic capacitor element is shown in FIG. 1. The solid electrolytic capacitor element 1 in FIG. 1 has a structure that contains a solid electrolyte layer 13, a carbon layer 14, and a conductive layer 15 on an oxide film 12 that has been formed on the surface of a sintered body 11 produced by sintering a valve action metal such as tantalum, niobium, titanium, or aluminum. This sintered body 11 is used as an anode body, while the oxide film 12 is used as a dielectric layer. The carbon layer 14 and the conductive layer 15 residing on the solid electrolyte layer 13 are used as a cathode.
The oxide film 12 is preferably provided by oxidation of the sintered body itself, but may be an oxide other than this.
Manganese dioxide or a conductive polymer is widely used as the solid electrolyte layer 13.
The carbon layer 14 is generally formed by applying and drying a carbon paste that has been prepared by dispersing a carbon powder in a vehicle that contains a resin (also referred to as a binder resin) and a solvent. It is thought that this carbon layer 14 can lower the contact resistance between the solid electrolyte layer 13 and the conductive layer 15 and lower the ESR.
The conductive layer 15 is generally formed by applying, and drying and/or curing a conductive paste that has been prepared by dispersing a metal powder, e.g., of silver, in a vehicle.
Such solid electrolytic capacitor elements provided with a carbon layer and a conductive layer, as described in Patent Document 1 and Patent Document 2, are already widely known.